1. Technical Field
The present disclosure relates to a stacked assembly of an integrated device of a microelectromechanical type, referred to in what follows as MEMS (Micro-ElectroMechanical System).
2. Description of the Related Art
In the field of integrated devices there is a desire for size reduction in order to meet the increasingly stringent requisites of miniaturization, in particular in the field of portable apparatuses.
As it is known, a MEMS integrated device in general comprises: a first body (usually defined as “die”) including semiconductor material (for example, silicon), integrating a micromechanical structure, operating for example, as a sensor for one or more quantities to be detected (for example, for providing an accelerometer, a gyroscope, a magnetometer, etc.) and generating an electrical quantity that is a function of the quantity to be detected (for example, a capacitive variation, a variation of electrical resistance, etc.); and at least one second die including semiconductor material (for example, silicon), integrating at least one electronic component or circuit, designed to be electrically coupled to the micromechanical structure so as to co-operate functionally therewith. Typically, the second die integrates an ASIC (Application-Specific Integrated Circuit), electrically coupled to the micromechanical structure, having, for example, the function of reading the electrical quantity detected by the micromechanical structure, where the structure operates as a sensor (for example, for carrying out operations of amplification and filtering of the detected electrical quantity).
A covering structure, or cap, is moreover provided in the MEMS integrated device, mechanically coupled on top of the first die integrating the micromechanical structure, with functions of protection for the same micromechanical structure. When the micromechanical structure have moving elements, for example, a beam or a membrane, designed to undergo deformation as a function of the quantity to be detected, the covering structure may have at least one cavity, provided above the moving elements, so as to define an empty space that ensures the freedom of movement and does not alter deformation thereof. Moreover, an access duct may possibly be formed through the covering structure, where a fluid connection with the outside (for example, for entry of pressure waves or acoustic waves) is utilized.
A MEMS integrated device generally also includes a package, i.e., a container or housing that surrounds, totally or in part, the dice of the device, enabling electrical connection thereof from the outside. The assembly of the MEMS integrated device, within the corresponding package, is usually defined as “chip” and may, for example, be electrically connected to a printed circuit board of an electronic apparatus in which the MEMS integrated device is to be used.
For example, a known package structure, defined as “wafer-level package” or “substrate-level package”, envisages the presence of a base substrate, to which the dice of the MEMS integrated device are coupled and which carries appropriate electrical contacts for electrical connection to the outside world, and of a protection coating, so-called “mold compound” formed directly on top of the base substrate and the dice, having coating and mechanical protection functions.
Traditionally, the dice of the MEMS integrated devices, integrating the respective micromechanical structure and ASIC, were set alongside one another on the inner surface of the base substrate of the package (i.e., the surface not facing the outside of the same package).
In order to reduce the lateral dimensions (i.e., the dimensions in a horizontal plane, parallel to the main plane of extension of the base substrate), stacking in the vertical direction (i.e., orthogonal to the horizontal plane) has been proposed for the first die integrating the micromechanical structure (with associated covering structure) and the second die integrating the ASIC.
This solution, although enabling the desired reduction of the lateral encumbrance, involves an increase in the overall thickness in the vertical direction that may be incompatible with some applications, in particular with applications of a portable type.
In fact, considering a typical thickness comprised between 400 μm and 420 μm for coupling between the first die integrating the micromechanical structure and the corresponding covering structure, and comprised between 80 μm and 280 μm for the thickness of the second die integrating the ASIC, and moreover considering the additional thickness represented by the package, with current techniques it is possible to obtain a minimum value of resulting thickness that is still rather high, ranging between 700 μm and 1000 μm.
To overcome at least in part this problem it has therefore been proposed to exploit the covering structure as active element in which to integrate the electrical/electronic components to be electrically coupled to the micromechanical structure in the first die (the second die being in this case absent in the assembly of the MEMS integrated device). This solution, although enabling a reduction of thickness equal to the thickness of the second die integrating the ASIC, is not, however, free from drawbacks.
In particular, the active use of the covering structure may prove to be difficult to implement, on account of the poor yield of the process of integration and of the imposed constraints as regards the usable dimensions.